1. Technical Field
This disclosure relates to an ultrasonic flowmeter, more particularly, a method and system for determining the density of a fluid flowing through a pipe within a pipe system.
2. Discussion of Related Art
The use of a non-intrusive Clamp-On Wide Beam ultrasonic flowmeter to measure both flow rate and liquid sonic propagation velocity of a liquid in a pipe is known.
A major attribute of the Wide Beam method is that the signal arrives at a point down the pipe wall essentially undistorted, with its amplitude reduced primarily by the extraction of the energy that has been injected into the liquid. There is no amplitude distortion due to internal pipe wall reflections. Accordingly, the measure of the amplitude of the received energy is a function of the energy delivered into the pipe wall.
The energy received by a transducer is dependent on the natural losses in the pipe wall. The natural losses are associated with the material between the transducers and as energy radiates in different paths than that which leads to the transducer. However, the additional loss due to the energy delivered into a liquid or other material inside the pipe will add to this loss. In addition, the received signal amplitude can be affected by other factors, such as a change in gain of an amplifier used to measure the received signal.
Therefore, a need exists to determine additional energy losses of the sonic energy waves, other than due to the presence of liquid, to establish a baseline against which to determine and accurately measure the density of a liquid flowing through a pipe.
According to an embodiment of the present invention, a system and method is provided which uses a non-intrusive Clamp-On Wide Beam ultrasonic signal to measure liquid density. As will be shown, the density of a liquid flowing through a pipe can be determined as a function of the measured sonic impedance of the container or pipe wall relative to the measured sonic impedance of the liquid divided by the measured liquid sonic propagation velocity of the fluid flowing through the pipe. In addition, a non-intrusive flowmeter can be used to measure the density of a fluid flowing through a pipe by extracting only those functions needed for measuring density, according to another embodiment of the present invention.
In reference to the problem of the received amplitude being affected by other factors, e.g. a change in gain of amplifier used to measure the received signal, the factors can be normalized by measuring the amplitude injected by a transmitter transducer as a reference. Thus, incorporating a reference receiver transducer in the transmitter transducer to determine the strength of transmission can do. An alternative method is to install a separate reference receiver transducer along the pipe wall disposed immediately adjacent to the transmitter transducer and a second receiver transducer, according to another embodiment of the present invention. By measuring the amplitude injected by a transmitter transducer as a reference factor, this will also incorporate any systematic change in the transducer to pipe wall sonic coupling.
Another embodiment of the present invention relates to a method for measuring the density of a fluid in a pipe. The method comprises the steps of determining a first, a second, and a third reference reading of a pipe using a transmitter transducer, a receiver transducer, and a primary receiver transducer coupled to a pipe, wherein the first reference reading is determined when the pipe is empty, the second reference reading is determined when the pipe contains a reference liquid of known sonic impedance within, and the third reference reading is determined when the pipe contains an unknown liquid within. Next, a liquid sonic propagation velocity of the unknown liquid is measured. The relationship between the impedance of the unknown liquid relative to the impedance of the reference liquid is determined. The density of the unknown liquid is measured by using the determined relationship of the unknown impedance to the known impedance of the reference liquid divided by the measured liquid sonic propagation velocity of the unknown liquid.
Further, another embodiment of the present invention relates to a system for measuring density of an unknown liquid having an unknown impedance flowing through a pipe. The system includes an ultrasonic transducer system coupled a pipe segment having a first end and a second end, the ultrasonic transducer system including a transmitter transducer disposed at the first end the pipe segment which generates and transmits sonic energy waves at a known desired rate, a reference receiver transducer disposed immediately adjacent to the transmitter transducer for receiving the sonic energy waves, and a primary receiver transducer disposed at the second end of the pipe segment for receiving the sonic energy waves. The system also includes a sensor for measuring an amplitude of the sonic energy waves at the reference receiver transducer and the primary receiver transducer of a plurality of reference fluids in a pipe system. And, a processor for recording the measured amplitude of the sonic energy waves at the reference receiver transducer and the primary receiver transducer to determine the ratio of the amplitude of the sonic energy waves received at the primary receiver transducer to the amplitude of the sonic energy waves received at the reference transducer and records the liquid sonic propagation velocity of a liquid and uses the ratios and liquid sonic velocity to determine density.
These and other objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings.